Method of restoring inked documents



Patented Dec. 5, 1939 UNITED STATES,

PATENT OFFICE METHOD OF BESTOBING INKED DOCUMENTS 3 'Claims.

Our invention relates to a method of restoring inked documents on which the ink has faded. Documents or papers restored according to our invention will not darken upon further aging.

6 It is also possible, according to our invention, to

impart a desired tint to the paper.

\ The characters written in iron ink on public and private documents or papersin time become so faded that they can be read only with difliculty 1 and in some instances the writings are entirely illegible. This is due to the iron ink having been oxidized to ferric oxide. In order to make such writings legible, it is customary to treat the documents or papers with chemicals so as to revivify the characters since most of the writings on old documents was done with the use of iron-tannin inks, they can be readily brought back to normal,'or even better than normal condition by the application of well known chemical laws. By treating the paper by immersing it in a water silution of potassium ferrocyanide acidifled. with a suitable acid such as, for example, acetic, phosphoric, hydrochloric or sulphuric, the ink is changed from itsiaded condition to one that is bright, clear and well defined. This change is due to the ferric oxide to which the ink has changed being converted into a bright precipitate of Prussian blue, which is a permanent color.

' The amount of potassium ferrocyanide in the solution may be varied to meet conditions, and modifiers, such as sodium chloride or potassium chloride, may be added to the solution if desired.-

Such modifiers tend to increase the permanence of the Prussian blue and-prevent edge blurring .35 of the characters.

The treatment which we have described will palred and in-time the'color of the paper may 'become'so pronounced as to entirely mask the 50 writing itself. 1 7

We have discovered a method of treating the documents to prevent these discolorations and herein lies our invention. After the writing-has been developed'in a suitable ferro-cyanide solutiom emlswashedinwaterasusualandthen is treated with a second solution which precipitates the ferrocyanide remaining in the paper as an insolublesalt and causes it to become per- I manently inactive and incapable of further reaction, thus preventing discoloration of the pa- 5 per. The latter solution, which is hereinafter referred to as a precipitating solution, consists of an organic or inorganic salt of a heavy metal selected from the group consisting of zinc, lead,

barium, cobalt, nickel, silver, cadmium, copper, 1

"silver, yellow; cadmium, yellowish; copper, redbrown; manganese, green-white. Inpractice, it will usually be found desirable to use a soluble 2 salt of zinc which'is at once cheap and gives a white insoluble precipitate. A solution of from 5 to 10% of zinc chloride, zinc sulphate,'.or zinc acetate has proved to be very satisfactory for the purpose. but it is to be understood that the g5 amount used may be varied, depending upon the paper and its tendency to discolor upon aging. The precipitate, namely zinc ferrocyauide, if a zinc salt is used, is white, insoluble and is not affected by long exposure to light. The excess 30 soluble zinc salt or any other soluble salt is washed away. v

In some instances, the paper may have a bluish tinge after treatment, which we may desire to change to white. In such a case, we can add a as suitable yellow dye,either of vegetable or coal tar origin, such as saffron, turmeric, annatto or auramine, naphthol yellow, sunset yellow or tartrazine. Other dyes may be used, so longas they are of such a character that they .are not pre- 40 cipitated by the metallic salt used in the precipitating solution. Such a dye will be hereinafter referred to as a modifying dye. The object of adding the modifying dye is to offset the blue background and change it to white. This is particularly useful where the paper itself has originally been discolored. By following the'teachings'of our-invention.- it is possible to treat documents on which the ink has faded and which have been revivifled by treat! ment with a ferrocyanide solution, so as to insure that the brilliance and permanence of the reviviiied characters will not be affected and that the paper itself will not be discolored with further Furthermore, the paper itself may, at the 86 :lametimebegivenadesiredpermanentcolora- While our invention has been described in connection with certain specific examples thereof, 8 itistobeunderstoodthatthesehave beenused for thepurpose oi illustration only and that the scope of the invention is not to be limited thereby.

We claim: 1. The method of reviviiying iron containing 10. faded characters on documents which consists in treating the characters with an acid solution 01' potassium terrocyanide, washing the paper, and subjecting the paper so treated to the action 01 a precipitatlhg solution which will cause the potas- 18 sium ierrocyanide remaining on the paper to be changed to an insoluble stable substance of a contrasting color to the revived characters, and washing the paper. r

- 2. The method of reviviiying i'aded iron tannin 99 characters on documents which consistsin treaton the paper to be changed to an insoluble stable 5 substance or a contrasting color'to the. revived characters, and washing the paper.

3. The method of reviviiying faded iron tannin ink characters on documents which consists in treating the documents with an acid solution of potassium ierrocyanide and thereafter treating the documents with a' precipitating solution to which has been added a modii'yins die the precipitating solution being of such a character that 15 it will precipitate the potassium. ierrocyanide re- 4 maining in the paper, as aninsoluble salt of a desirable color. A

ALEXANDER LOWY.

cums: n. 0mm. 10 

